1. Field of the Invention
The present invention relates generally to telecommunications systems and methods for positioning a mobile station within a cellular network, and specifically to providing encrypted network information to mobile stations for use in calculating the location of the mobile station.
2. Background and Objects of the Present Invention
Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to FIG. 1 of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and an integrated Visitor Location Register (VLR) 16 therein. The MSC 14 provides a circuit switched connection of speech and signaling information between a Mobile Station (MS) 20 and the PLMN 10. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which the MS 20 may move freely without having to send update location information to the MSC 14 that controls the LA 18. Each LA 18 is divided into a number of cells 22. The MS 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless.
The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several BTS""s 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.
With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information, for subscribers registered within that PLMN 10. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
Determining the geographical position of an MS 20 within a cellular network 10 has recently become important for a wide range of applications. For example, location services (LCS) may be used by transport and taxi companies to determine the location of their vehicles. In addition, for emergency calls, e.g., 911 calls, the exact location of the MS 20 may be extremely important to the outcome of the emergency situation. Furthermore, LCS can be used to determine the location of a stolen car, for the detection of home zone calls, which are charged at a lower rate, for the detection of hot spots for micro cells, or for the subscriber to determine, for example, the nearest gas station, restaurant, or hospital, e.g., xe2x80x9cWhere am Ixe2x80x9d service.
As can be seen in FIG. 2 of the drawings, upon a network positioning request, the MSC 14 obtains, from the serving BTS 24 and BSC 23, a Timing Advance (TA) value, which corresponds to the amount of time in advance that the MS 20 must send a message in order for the serving BTS 24 to receive it in the time slot allocated to that MS 20. The TA value, in turn, provides location information regarding the MS 20 location. This is due to the fact that when a message is sent from the MS 20 to the BTS 24, there is a propagation delay, which depends upon the distance between the MS 20 and the BTS 24. The TA values are expressed in bit periods, and can range from 0 to 63, with each bit period corresponding to approximately 550 meters between the MS 20 and the BTS 24.
This TA value is forwarded to a Serving Mobile Location Center (SMLC) 270 for use in assisting the calculation of the geographical location of the MS 20. It should be noted that the SMLC 270 can use a number of different positioning mechanisms, including, but not limited to, Time of Arrival (TOA), which is a network-based positioning method, Enhanced Observed Time Difference (E-OTD) and Global Positioning System (GPS), which are both MS-based positioning methods. After the SMLC 270 calculates the MS 20 location, this location can be sent to a Location Application (LA) 280 that requested the positioning. It should be noted that the requesting LA 280 could be located within the MS 20 itself, within the MSC 14 or could be an external node, such as an Intelligent Network (IN) node. If the LA 280 is not within the MS 20 or within the MSC 14, the location information is sent to the requesting LA 280 via the MSC 14 and a Gateway Mobile Location Center (GMLC) 290.
As mentioned above, two common types of MS-based positioning methods are the E-OTD method and the GPS method. For the GPS method, the MS 20 can have a Global Positioning System (GPS) receiver built into it, which is used to obtain positioning data, which is sent to the SMLC 270 to determine the location of the MS 20. For the E-OTD method, the MS 20 can collect positioning data based on the Observed Time Difference (OTD) between the time a BTS 24 sends out a signal and the time the MS 20 receives the signal. This time difference information can be sent to the SMLC 270 for calculation of the location of the MS 20, or the MS 20 itself, with knowledge of the location of the BTS 24, can determine it""s location. It should be noted that it is expected in the near future for the GPS receiver within the MS 20 to be able to calculate the MS 20 location.
By utilizing the E-OTD or GPS positioning method and implementing the location calculation functionality within the MS 20 itself, the location calculation can be performed even when the MS 20 is in idle-mode. However, for MS-based positioning methods, it is necessary that the MS 20 has knowledge of certain network information, such as the coordinates of a serving BTS 24. Although this network information can be broadcast over the Broadcast Control Channel (BCCH), many network operators may wish to avoid broadcasting such information for security reasons.
It is, therefore, an object of the present invention to encrypt and download network information, such as BTS coordinates, to MS""s that have location calculation capabilities.
It is a further object of the present invention to allow the MS to decrypt the network information in order to use this network information in calculating the MS location information.
It is still a further object of the present invention to make the MS decryption ability dependent upon either the number of positionings originally requested or the duration of the positioning requested.
The present invention is directed to telecommunications systems and methods for downloading encrypted network information, such as BTS coordinates, in a point-to-point manner between the network and the MS with location calculation capabilities. When an MS registers with the network, the MS shall indicate as part of the xe2x80x9cearly classmarkxe2x80x9d process its location calculation capabilities and the type algorithm to be used for decrypting the network information. As a result of a mobile originating request for assistance data, the network shall encrypt and download the network information to the MS. The mobile originating request for assistance data shall also request from the network the location deciphering key KL, and shall also indicate the number of positionings and/or the duration of the positioning to be performed by the MS. A subscriber identification key Ki retrieved from HLR, along with a non-predictable random number and the number and/or duration of positionings provided by the MS shall be used as input to a new algorithm to derive a location deciphering key KL. Using the derived key KL, the network information is ciphered by the MSC and transmitted to the MS. The MS uses the Ki, stored therein, and the random number, which is transmitted to the MS from the MSC, along with the new algorithm for deciphering network information and the number and/or duration of positionings requested by the MS to produce the KL, which is used by the MS to decipher the network information. In addition, the number of positionings and/or the duration of the positioning is constantly compared by the MS with the KL, and if the requested limit is reached, the KL becomes invalid and the MS can no longer decipher the broadcasted encrypted network information. Advantageously, the encryption and deciphering process of the present invention can be utilized by the network to charge a mobile subscriber either on a per positioning request basis or on a positioning duration basis.